Place sausage in a large, deep skillet. Cook over medium high heat until evenly brown.
Remove sausage, drain and set aside.
Pour off most of the fat from the pan, leaving about 2 to 3 tablespoons. Return pan to medium-low heat and add flour. Using a whisk, stir vigorously until roux forms, scraping bottom of pan. Reduce heat to low and let roux cook at least 5 minutes, stirring occasionally. Grandma always "burned" hers a little on purpose.
Add milk in a stream, whisking the whole time. After adding about 2 1/2 cups, turn heat to medium and continue cooking, stirring constantly. Bring gravy to a boil and cook to desired thickness.
Add more milk if a thinner gravy is desired. You may also add some of the cooked and crumbled sausage to the gravy.
